The cautious person scratches his chin, nods and says nothing for a moment. Then he or she says something vague yet wise, beginning with, "Yes, yes ... however--" and ending with a nod to time as the ultimate judge of whether, in this case, it's a good idea to build a slender, swirling skyscraper...

2,000-foot Chicago skyscraper A developer's proposal for a twisting 115-story spire near Navy Pier would forever change Chicago's skyline, with architect Santiago Calatrava's design bringing the city into the 21st Century.

Whatever happened to the post-9/11 fear of high-rises? Plans to build the nation's tallest building at Lake Shore Drive and the Chicago River immediately raised questions about whether the 115-story residential tower would be an attractive target for a terrorist attack. But experts put terrorism...